This invention relates to an improved encoder for indicating angular position or rotation of a shaft, and particularly a digital encoder for use with materials handling vehicles.
Material handling vehicles have used analog devices for indicating the position of various shaft positions, such as control devices. These analog devices, such as potentiometers, provide an absolute indication of position, however, these devices are subject to drift from age or heat and thus do not always provide the desired accuracy needed for some control functions. Conventional optical encoders for converting rotational motion of a shaft into digital signals typically include an encoder disc having rotation indicating track means provided with a plurality of spaced apart markings. These markings may take several forms, such as individual marks or pairs of equally spaced but offset, equally spaced apart marks on adjacent tracks. They are often optically detected by photoelectric means.
Digital encoders may include a pair of tracks where the coded marks alternate in order to provide an output signal indicating both the amount and the direction of rotation. In some encoders, an index track is provided with an index mark to provide a reference, as for example when the encoder is used in an application where it is necessary to determine a reference or neutral position of the shaft connected to the encoder.